/in/foo.cc: In function 'int main()':
/in/foo.cc:23:20: warning: unknown conversion type character 0x2 in format [-Wformat=]
     printf("%\2f",r); 
                    ^
/in/foo.cc:23:20: warning: too many arguments for format [-Wformat-extra-args]
/in/foo.cc:23:11: warning: 'r' may be used uninitialized in this function [-Wmaybe-uninitialized]
     printf("%\2f",r); 
     ~~~~~~^~~~~~~~~~